function Food(el)
{
    // 保存地图对象
    this.el = el
    // 保存食物属性
    this.len = 20
    this.foodObj = null
    this.foodX = 0
    this.foodY = 0
}
Food.prototype.create = function()
{
    // 1.创建div标签对象
    let divObj = document.createElement('div')
    // 2.设置样式(w20/h20/bggreen/position:absolute)
    divObj.style.width = this.len + 'px'
    divObj.style.height = this.len + 'px'
    divObj.style.background = 'green'
    divObj.style.position = 'absolute'
    divObj.style.borderRadius = '50% 50%'
    // 单独保存下食物的对象
    this.foodObj = divObj
    // 3.页面展示
    this.el.appendChild(divObj)
    // 4.默认移动食物
    this.move()
}
Food.prototype.move = function()
{
    let foodXMaxNum = this.el.clientWidth / this.len - 1
    let foodYMaxNum = this.el.clientHeight / this.len - 1
    //产生随机蛇(坐标)
    this.foodX = Math.floor(Math.random() * (foodXMaxNum-0+1)+0) * this.len
    this.foodY = Math.floor(Math.random() * (foodYMaxNum-0+1)+0) * this.len
    
    this.foodObj.style.left = this.foodX + 'px'
    this.foodObj.style.top = this.foodY + 'px'
}